A conventional OEIC which receives light from an optical fiber and converts the optical signal to an electrical signal comprises an optical fiber fixing groove for fixing an optical fiber and facilitating the introduction of light into a photodiode and a light receiving IC section, the optical fiber fixing groove and the light receiving IC section being provided on a common silicon substrate.
Conventional OEICs include, for example, a semiconductor device disclosed in Japanese Patent Application No. 52700/1995. This OEIC comprises an optical fiber fixing groove for fixing an optical fiber, a photodiode for converting an optical signal output from an optical fiber to an electrical signal, and a receiving IC for processing a signal which has been converted from an optical signal to an electrical signal by the photodiode, and a plurality of channels of this structure are provided in parallel on a common substrate.
When the OEIC is applied in this way to a parallel light receiving IC for processing lights transmitted in parallel respectively for a plurality of channels, an electrical signal generated in a transistor within one channel interferes with another channel to produce a noise, that is, unfavorably resulting in crosstalk. In order to reduce the influence of the crosstalk, for example, an attempt has been made to increase the capacity component between light receiving IC sections for respective channels by newly providing a trench for element separation on the outermost periphery of the light receiving IC sections or to delay the propagation of the noise by increasing the distance between the light receiving IC sections.
In the conventional parallel light receiving IC, the additional provision of a trench for element separation around the receiving IC sections cannot fully prevent the influence of the crosstalk. This is because the trench for element separation has a dimension of not more than 1 .mu.m in width and 10 .mu.m in depth which is unsatisfactory for preventing noises from propagating through the substrate.
Further, the distance between ICs for respective channels in the parallel light receiving IC cannot be increased without any restriction because an excessive increase in the distance between ICs for respective channels results in increased chip size, which is disadvantageous for integration.